The present invention relates to oscillators and, more particularly, to a crystal controllable oscillator.
Crystal controlled oscillators that are suited to be manufactured in monolithic integrated circuit form and operated as voltage controlled oscillators (VCO's) are well known to those skilled in thee art. For instance, U.S. Pat. No. 4,571,558 describes such an oscillator. The oscillator circuit disclosed in the '558 patent requires only one additional external pinout from the integrated circuit for connection to an external crystal resonator network. This oscillator includes an oscillation sustaining feedback loop comprising a pair of integrators connected between the output of a differential amplifier and an input thereof for introducing the correct phase shift therebetween to maintain oscillation.
Based on the prior art there is a need for an improved integrated crystal controlled oscillator having a simplified structure to increase manufacturing yields to decrease production costs as well as having improved frequency stability and the ability to drive emitter-coupled-logic loads.